Crystalline aluminosilicates, or zeolites, of which mordenite is one example, are well known in the art and have found extensive application as hydrocarbon conversion catalysts or as a component thereof. Such materials are of ordered crystalline structure often visualized as a three-dimensional network of fundamental structural units consisting of silicon-centered SiO.sub.4 and alumnum-centered AlO.sub.4 tetrahedra, the tetrahedra being interconnected by a mutual sharing of apical oxygen atoms and arranged to form cages or cavities in open communication through smaller intracrystalline channels or pore openings whose narrowest cross section has essentially a uniform diameter characteristic of each crystalline aluminosilicate variety. To effect a chemical balance, each AlO.sub.4 tetrahedra has a cation associated therewith--usually a sodium or other exchangeable cation. The aforementioned cages or cavities are occupied by water molecules and by the last mentioned cations, both of which exhibit considerable freedom of movement permitting ion-exchange and reversable dehydration.
The crystalline aluminosilicates, or zeolites, employed in the manufacture of the catalytic composite of this invention, are of the mordenite crystal structure, highly siliceous in nature and generally characterized by a silica-alumina mole ratio of from about 6 to about 12 as found in nature. The mordenite crystal structure comprises four- and five-membered rings of the SiO.sub.4 and AlO.sub.4 tetrahedra so arranged that the crystal lattice comprises pores and channels running parallel along the crystal axis to give a tubular configuration. This structure is unique among the crystalline aluminosilicates since the channels or tubes do not intersect, and access to the cages or cavities is in only one direction. For this reason, the mordenite structure is frequently referred to as two-dimensional. This is in contrast to other well-known crystalline aluminosilicates, for example faujasite, in which the cavities can be entered from three directions. Mordenite, clinoptilolite, or mordenite which has been synthesized or acid extracted, caustic extracted or otherwise treated to increase the silica-alumina mole ratio to about 20:1 or more while maintaining the mordenite crystal structure, may be used in the manufacture of the catalytic composite of this invention.
Crystalline aluminosilicates having a mordenite crystal structure have heretofore been utilized composited with a refractory inorganic oxide, typically alumina, as a hydrocarbon conversion catalyst, and are particularly useful with respect to the transalkylation of alkylaromatic hydrocarbons.
It is an object of this invention to present a new and useful method of manufacture providing a novel catalytic composite of improved selectivity.
In one of its broad aspects, the present invention embodies a method of manufacture providing a catalytic composite of improved selectivity which comprises subjecting a mordenite alumina to an aqueous ammoniacal treatment at a pH of at least about 9.5; calcining the resulting mordenite alumina from step (a); subjecting the resulting calcined mordenite alumina to an aqueous solution containing a boron salt; and calcining the resulting mordenite alumina from step (c) to provide said catalytic composite.
Other objects and embodiments of this invention will become apparent in the following detailed specification.